<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>函数</title>
    <script>

        /**
         * 在js中变量在以下集中情况会人为是false
         *
         * false
         * 0
         * Nan
         * undifed
         *
         *
         * */

        function yun9(a=30, b=60) {

            console.log(a + "+" + b + "=" + (a + b));
        }

        yun9();
        yun9(5);
        yun9(0, 0);
        yun9(5, 10, 15);
    </script>
</head>
<body>

</body>
</html>